The present invention relates to communications devices and more particularly to a coupler or interface unit for providing bidirectional data transfer between a host and a remote processor.
During normal communications between a host and a remote processor, the various data transfers necessary in both directions are effected by means of normal handshaking signals which couple the remote and host processors so as to provide such communication. However, there are conditions wherein the remote processor may have been disabled and accordingly the host is not able to communicate with the remote processor. In certain situations, such a condition may be catastrophic and is accordingly undesirable. For example the remote processor may have had a system software failure or for some other reason may to a certain extent be unusable. In addition, the remote processor may have been stopped and may have to be restarted from a remote location such as the host processor. Accordingly, it is desirable to include means in the system, responsive to the host processor, for enabling data transfer in either direction. This requirement for providing such communication in spite of such possible failures is additionally complicated where word lengths normally processed by the host processor and the remote processor are different.
It is accordingly an object of the invention to provide improved means for providing bidirectional communications between a host and a remote processor particularly where the remote processor may to a certain extent be disabled and is unable to provide the normal signals to effectuate such transfer.
It is a further object of the invention to provide a capability of enabling such bidirectional data transfer while handling different size words that are normally processed in the respective processors.